1. Field of the Invention
The present invention relates to a thin film transistor substrate having a thin film transistor (TFT) and a capacitor formed in the substrate, a defect repairing method therefor, and a display device.
2. Description of the Related Art
Flat-panel type display devices that are now becoming the mainstream of display devices include liquid crystal display devices, plasma display devices, organic EL (Electro Luminescence) display devices and the like. Some of these devices use a thin film transistor substrate (hereinafter referred to also as a “TFT substrate”) in which substrate a driving circuit including a TFT is formed. The TFT substrate is obtained by forming the film of a wiring layer and a semiconductor layer on a substrate mainly made of a glass plate by sputtering or CVD (Chemical Vapor Deposition), and patterning the film by photolithography to form a TFT circuit and a wiring pattern.
In a process of manufacturing the TFT substrate, foreign matter referred to as dust may result in a missing pattern or an excess residue. Such missing patterns (open defects) or excess residues (short defects) are collectively referred to as defects, and cause a circuit disconnection or a short circuit. As a result, various display abnormalities occur, such as a pixel dark dot (non-emitting dot defect), a pixel bright dot (dot defect of emitting light at all times or emitting noticeably brighter light than the periphery), a dark line (non-emitting line defect), a bright line (line defect of emitting light at all times or emitting noticeably brighter light than the periphery), an entire-surface display abnormality, or the like. Excluding a limited number of pixel dark dots, a display device having such a display abnormality is regarded as a defective, and cannot be shipped as a product.
Therefore, in a process of mass-producing the TFT substrate, a pattern defect is detected by using an optical inspection device, an electrical inspection device or the like, and a defect repair is made on the basis of a result of the detection to normalize the operation of the TFT substrate, or an abnormality alleviating measure such, for example, as making pixel bright dots or a bright line dark dots is taken.
One of repairing methods bridges disconnected parts to achieve conduction (connection type repair). As the bridging method of the connection type repair, a chemical vapor thin film forming (laser CVD) system using laser light, a conductive thin film transfer (laser transfer) system using laser light, and a system using a conductive micro-paste have been developed and put to practical use.
When an open defect is repaired by the connection type repair, patterns at both ends of the open defect may be directly connected to each other, or may be connected to each other via patterns connected to the patterns at both ends. In either case, the patterns to be connected need to be directly exposed on a surface, or need to be exposed under an insulating layer without being covered by another pattern.